The present invention relates to a wrench for use in fastening or unfastening bolts or nuts, and more particularly, to an impact wrench. More specifically, the present invention relates to an impact wrench whose operation is automatically stopped when the fastener is fully tightened.
A conventional impact wrench has a hammer carried on a rotor driven by a motor, which hammer is caused to rotate in association with the rotor during which the hammer repeatedly engages and disengages an anvil, thereby transmitting impacts thereto. Such impact wrenches are widely used in the component assembling lines, particularly in the automobile assembling line. The impact wrenches are operated by workers, wherein the extent of the fastening force depends on their personal fingers' touch. As a result, the period of time for fastening is likely to differ from operator to operator. Undesirable variations in fastening bolts or nuts has occurred.